Effect of thermal cycling on the transformation temperatures of TiNi alloys

Miyazaki, S.; Igo, Y.; Otsuka, Kazuhiro

doi:10.1016/0001-6160(86)90263-4

Cited by 437 publications

(256 citation statements)

References 11 publications

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“…The stabilisation of transformation temperatures by prior cold work is demonstrated by a previous finding of Miyazaki et al [4] [5]. This involved pre-straining a 49.8at.%Ni alloy with no previous cold work so that a residual plastic strain could be measured after unloading.…”

Section: Thermal Cyclingmentioning

confidence: 88%

“…However, careful analysis of previous papers helps explain why anomalies are found when analysing thermal cycling effects. Where authors find decreasing M s temperatures [4] [6] it tends to be associated with pure thermal cycling or very low stress levels and implies that dislocations within the microstructure interfere with the transformation and increase the degree of under-cooling required for the transformation to proceed. Similarly, where authors find increasing M s temperatures [6] [7][8] it tends to be associated with an applied stress either prior to or during thermal cycling.…”

Section: Thermal Cyclingmentioning

confidence: 99%

“…Although cycling effects are attributed to dislocation generation [9][10] defect redistribution [11], or both [11], very little confirming evidence is ever provided although it has been shown by transmission electron microscopy that dislocations are generated during stress free transformation cycling [4]. It is obvious how complicated dislocation arrays generated during stress free cycling may interfere with the transformation accommodation mechanism thus reducing the M s temperature.…”

Section: Thermal Cyclingmentioning

confidence: 99%

See 2 more Smart Citations

A review of shape memory stability in NiTi alloys

Morgan

Friend

2001

J. Phys. IV France

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Stability and fatigue are terms often referred to when discussing the durability of the shape memory effect. This paper considers the meaning of these terms and how they relate to the macroscopic memory response and the microstructural accommodation response of NiTi alloys. The results of previous workers are analysed and compared to establish how the three parameters that apparently control the macroscopic memory effect -temperature, stress and strain, are controlled themselves by the alloy's microstructure. It will be shown that repeated phase changes will alter the microstructure and hysteresis of the transformation and in turn this will lead to changes in transformation temperatures, transformation stresses and transformation strains. Both superelastic and memory effects are considered simultaneously so as to emphasise the similarities between the respective stress/strain and strain/temperature degradation effects. Although the mechanisms of both are often regarded as physically separate it is shown that in fact the macroscopic changes observed during cycling are a result of similar microstructural changes. It is also shown how as a result of the inherently large transformation strains internal cracking may occur and that even apparently stable microstructures can fail catastrophically via conventional crack growth mechanisms.

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Section: Thermal Cyclingmentioning

confidence: 88%

Section: Thermal Cyclingmentioning

confidence: 99%

Section: Thermal Cyclingmentioning

confidence: 99%

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A review of shape memory stability in NiTi alloys

Morgan

Friend

2001

J. Phys. IV France

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“…Functional fatigue of NiTi shape memory alloys is often associated with the introduction of dislocations during cycling. It is well known that with thermal cycling of NiTi shape memory alloys the dislocation density increases [8] and the martensite start temperature (M s ) decreases. Chumlyakov et.…”

Section: Introductionmentioning

confidence: 99%

In-situ TEM cooling/heating experiments on deformed NiTi shape memory single crystals

Simon

Kröger

Somsen

et al. 2009

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

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Abstract. In the present study we report about the influence of dislocations on martensitic transformations in NiTi single crystals. Microstructural investigations are performed on Ni 50.4 Ti 49.6 (at.%) single crystals using in-situ cooling and heating transmission electron microscopy (TEM). Solution heat-treated Ni 50.4 Ti 49.6 single crystals were oriented by electron backscatter diffraction (EBSD) and compressed in [111] B2 -direction to different strain levels. DSC measurements on undeformed and deformed material states reveal a two step transformation from B2 to R-phase and then from Rcrystal shows that mainly screw dislocations with [001] type burgers vectors are present. During cooling, the martensitic R-phase grows homogeneously. On further cooling in some regions a burst like growth of B19'-neddles can be observed in addition to B19'-regions that nucleate and grow promoted by the stress-fields of dislocations. Dislocation analysis after back transformation suggests that dislocations form as a result of the martensitic transformation.

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“…The evolution of the martensitic transformation during thermal cycling (repetition of the temperature induced transformation) in NiTi alloys has hccn studied in several works [1,2]. A decrease of transformation temperatures of about 30-40K has hecn observed after the first 10-20 cycles in annealed specimens, whereas in he case of' Ni-rich aged specimens, containing dispersions of fine precipitates inside the B 2 matrix, the effect of thermal cycling is much less pronounced [I].…”

Section: Introductionmentioning

confidence: 99%

Study of Dislocations Generated by Thermal Cycling in Ni-Ti-Co Shape Memory Alloys

et al. 1995

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Abstract. In the present work we report some results concerning the evolutions of transformation temperatures and microstructure during thermal cycling in Ti-47%Ni -3% Co (atomic percent). In the case of hulk material (obtained by a conventional solidification method) high amounts of dislocations l'onn during cycling, which produce a considerable evolution of the transformation temperatures (up LO -40K). wl~ile in mcltspun material containing a dispersion of fine precipitates, the formation 01' dislocations during thermal cycling is highly reduced, giving rise to stable transformation temperatures. The dislocation characteristics have been analysed by means of two-beam condition observations as well as the Large Angle Convergent Beam Electron Diffraction technique. Some energetical considerations concerning the dislocations are pointed out to interpret the evolution of transformation temperatures.

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Effect of thermal cycling on the transformation temperatures of TiNi alloys

Cited by 437 publications

References 11 publications

A review of shape memory stability in NiTi alloys

A review of shape memory stability in NiTi alloys

In-situ TEM cooling/heating experiments on deformed NiTi shape memory single crystals

Study of Dislocations Generated by Thermal Cycling in Ni-Ti-Co Shape Memory Alloys

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